Tadalafil: what the human evidence actually shows
Tadalafil is a phosphodiesterase type-5 (PDE5) inhibitor, FDA-approved for erectile dysfunction, benign prostatic hyperplasia and pulmonary arterial hypertension. Its distinguishing feature is duration: a half-life of roughly 17.5 hours gives it an effective window of up to 36 hours, which is why it is often called 'the weekend pill'. It is available as a low-cost generic.
What the evidence actually shows
The evidence base is large, old and solid. Tadalafil is effective for erectile dysfunction across multiple well-powered randomised trials, and its efficacy for BPH symptoms is also established. This is genuinely one of the best-evidenced treatments discussed anywhere on this site — a marked contrast to the peptides.
Absolute versus relative: reading the number correctly
Trial results are usually reported as relative figures, because relative figures are larger and therefore more persuasive. A "20% reduction in cardiovascular events" sounds transformative. The absolute reduction in SELECT was from 8.0% to 6.5% — about 1.5 percentage points over roughly three years. Both statements describe the same result honestly; only one of them tells you what to expect for yourself.
The same applies to weight-loss figures. A mean reduction of 20.9% is a mean. Individual results in these trials ranged from substantial loss to none at all, and a mean tells you nothing about where you personally would land. Anyone quoting a trial average as a promise is misusing it.
Funding and conflicts of interest
Every pivotal trial in this field was funded by the company that manufactures the drug it tested. That is normal in pharmaceutical research and it does not make the results false — these are large, well-conducted, peer-reviewed studies. It does mean the funding belongs in the citation every time, particularly for head-to-head trials where the funder makes the winning drug. SURMOUNT-5 was funded by Eli Lilly and found Lilly's drug superior. The result is plausible and consistent with the separate trial programmes; the disclosure still belongs beside it.
Where this sits against the other evidence
No single trial should be read alone. The strength of the GLP-1 evidence base is that multiple independent trial programmes — SURMOUNT for tirzepatide, STEP for semaglutide, SCALE for liraglutide, SELECT for cardiovascular outcomes — point in a consistent direction across tens of thousands of participants. That consistency is what makes the class credible.
What that consistency does not do is extend to products the trials never tested. Every one of those programmes studied an FDA-approved subcutaneous injection. None studied a compounded preparation, a microdose regimen, or an orally disintegrating tablet. The evidence is strong exactly where it was collected and silent everywhere else, and the gap between those two things is where most of the marketing in this industry operates.
Frequently asked questions
What does Tadalafil cost through telehealth?
It is available as an inexpensive FDA-approved generic — price that at a pharmacy before paying a subscription for a compounded version.
Is Tadalafil FDA-approved?
Tadalafil is FDA-approved and is available as an inexpensive generic. This is one of the few areas on this site where the FDA-approved product is also the cheap one, and the practical advice is simple: there is usually no good reason to buy a compounded or 'propriet
Does Tadalafil work?
The evidence base is large, old and solid. Tadalafil is effective for erectile dysfunction across multiple well-powered randomised trials, and its efficacy for BPH symptoms is also established. This is genuinely one of the best-evidenced treatments discussed anywhere on this site
Sources
- U.S. Food and Drug Administration — approved labels and compounding guidance for this molecule.
- PubMed / NIH — indexed human clinical literature.
- ClinicalTrials.gov — registered trials, where they exist.
- Our source hierarchy and pricing-verification methodology.
Jastreboff AM et al., N Engl J Med 2022 (NCT04184622), n=2,539. Dose-response is real: the effect rises with dose. These are FDA-APPROVED SUBCUTANEOUS INJECTION doses — they do not transfer to compounded, microdose or ODT products. Trial means are not individual promises.
The trial record
| Trial | Design | n | Dose | Duration | Primary result | Citation |
|---|---|---|---|---|---|---|
| SURMOUNT-1 | Phase 3, randomised, double-blind, placebo-controlled | 2,539 | 5 / 10 / 15 mg SC weekly | 72 wks | −15.0% / −19.5% / −20.9% vs −3.1% placebo | Jastreboff, NEJM 2022; NCT04184622 |
| SURMOUNT-2 | Phase 3, RCT, in type 2 diabetes | 938 | 10 / 15 mg SC weekly | 72 wks | −12.8% / −14.7% vs −3.2% placebo | Garvey, Lancet 2023; NCT04657003 |
| SURMOUNT-3 | Phase 3, RCT, after 12-wk intensive lifestyle lead-in | 806 | Max tolerated (10/15 mg) | 72 wks | −18.4% additional, vs +2.5% placebo | Wadden, Nat Med 2023; NCT04657016 |
| SURMOUNT-4 | Randomised WITHDRAWAL after 36-wk open-label lead-in | 670 | Max tolerated | 88 wks | Continue: −5.5% further. Withdraw to placebo: +14.0% REGAINED | Aronne, JAMA 2024; NCT04660643 |
| SURMOUNT-5 | Phase 3b, OPEN-LABEL, active-controlled head-to-head | 751 | Max tolerated vs semaglutide | 72 wks | −20.2% vs semaglutide −13.7%, p<0.001 | Aronne, NEJM 2025; NCT05822830 |
| SURPASS-2 | Phase 3, RCT, type 2 diabetes, active-controlled | 1,879 | 5 / 10 / 15 mg vs semaglutide 1 mg | 40 wks | HbA1c −2.01 to −2.30% vs −1.86% | Frías, NEJM 2021; NCT03987919 |
| SURPASS-CVOT | Phase 3, cardiovascular outcomes, vs dulaglutide | 13,299 | Max tolerated | ~4.5 yrs | Non-inferior for MACE; not superiority vs placebo | Nicholls, 2024; NCT04255433 |
1. They are means, not promises. A −20.9% mean in SURMOUNT-1 contains people who lost far more and people who lost almost nothing. A trial average tells you what happened to a population; it does not tell you what will happen to you.
2. Every one is an FDA-APPROVED SUBCUTANEOUS INJECTION. No trial in this table tested a compounded preparation, a microdose regimen, or an orally disintegrating tablet. When these figures appear on a page selling a compounded ODT, evidence has been moved across a dosage form without justification.
3. All were funded by Eli Lilly, which manufactures tirzepatide. That is normal in drug development and does not make the results false — these are large, peer-reviewed studies. It belongs in the citation anyway, and it matters most in SURMOUNT-5, where the funder made the winning drug and the trial was open-label.
Jastreboff AM et al., N Engl J Med 2022, n=2,539 (NCT04184622). The effect rises with dose — which is precisely why a ~1mg 'microdose' cannot be expected to produce the headline result. FDA-approved subcutaneous injection.
The evidence is strong exactly where it was gathered and silent everywhere else. The gap between those two things is where most of the marketing in this industry operates, and recognising it is the single most useful skill a patient in this market can have.
Dosing, titration, and what it does to your bill
| Period | Dose | What it is for |
|---|---|---|
| Weeks 1–4 | 2.5 mg | Tolerance-building only. This dose is not intended to produce weight loss. If your provider's price is quoted at 2.5 mg, that is not the price of treatment. |
| Weeks 5–8 | 5 mg | First therapeutic dose (−15.0% in SURMOUNT-1). |
| Weeks 9–12 | 7.5 mg | Escalate only if tolerated. |
| Weeks 13–16 | 10 mg | A common maintenance dose (−19.5%). |
| Weeks 17–20 | 12.5 mg | Escalate only if tolerated. |
| Week 21+ | 15 mg | Maximum maintenance dose (−20.9%). |
The advertised price is usually the 2.5 mg price. On a programme that escalates with dose, the rate you are quoted at signup is for a dose the label explicitly describes as a starting dose — not a treatment dose. Ask what you will pay at 10 mg, and compare that number instead.
A 'microdose' of ~1 mg/week sits below every dose in SURMOUNT. The trials used 5, 10 and 15 mg. A microdose is not a discounted route to the SURMOUNT result; it is a different product with a smaller expected effect and no equivalent trial evidence.
Safety, contraindications and monitoring
Tirzepatide carries a boxed warning for thyroid C-cell tumours, based on rodent data. It is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. This is not a precaution to weigh; it is a hard stop.
Serious but less common risks include pancreatitis, gallbladder disease (cholelithiasis and cholecystitis), acute kidney injury secondary to dehydration from vomiting or diarrhoea, diabetic retinopathy complications in people with existing retinopathy, and hypoglycaemia when combined with insulin or a sulfonylurea. Severe abdominal pain radiating to the back warrants urgent assessment for pancreatitis, not a message to a chat widget.
Before starting, a clinician should establish a baseline: weight and BMI, blood pressure, HbA1c or fasting glucose, a lipid panel, and renal and hepatic function. During treatment, tolerance should be reviewed at each escalation step rather than escalated automatically on a calendar.
Percentage of participants reporting each event. Gastrointestinal effects dominate, are usually mild-to-moderate, and are most pronounced during dose escalation. Source: SURMOUNT-1, N Engl J Med 2022.
Discontinuation: what the withdrawal trial found
Aronne LJ et al., JAMA 2024, n=670 (NCT04660643). After a 36-week open-label lead-in, participants randomised to placebo regained ~14% of body weight over the following 52 weeks; those who continued lost a further ~5%. This is the single most important trial for understanding the true cost of treatment.
In SURMOUNT-4 — the randomised withdrawal trial — participants taken off tirzepatide after a 36-week lead-in regained roughly 14% of body weight over the following year, while those who continued lost a further ~5%. This is the trial that most changes the arithmetic of treatment, and it is almost never cited on a pricing page.
The consequence is financial as much as clinical. If holding the result requires holding the medication, then the figure that matters is not the introductory price, and not even the annual price. It is the indefinite monthly price. Anyone selecting a provider on the strength of a first-month rate is optimising the wrong variable entirely.
Questions to ask your clinician
- Given my history — specifically thyroid, pancreatic and gallbladder — is a GLP-1 appropriate for me at all?
- What baseline laboratory work will you order before I start?
- What is my target dose, and how quickly will we escalate?
- Which side effects should make me call you rather than wait it out?
- What is the plan for maintenance, and what happens if I stop?
- Will I see the same clinician at each follow-up, or a different one each time?
Compounded, brand, microdose, ODT — four different products
These words are used interchangeably in marketing and they are not interchangeable at all. The distinction decides what evidence applies to what you are actually buying.
| Product | Regulatory status | Trial evidence |
|---|---|---|
| Brand Zepbound / Mounjaro (injection) | FDA-approved. Reviewed for safety, effectiveness and quality before marketing. | Direct. SURMOUNT and SURPASS tested exactly this product. |
| Brand Foundayo (oral, orforglipron) | FDA-approved. Its own trial programme. | Direct, for that product. |
| Compounded tirzepatide (injection, full dose) | NOT FDA-approved. No premarket review of safety, effectiveness or quality. | None for the compounded product itself. Same molecule, same route — but the product in your hand was never in a trial. |
| Microdose (~1 mg/wk) | NOT FDA-approved. | None. Sits BELOW every dose in SURMOUNT (5/10/15 mg). Expect a smaller effect. |
| ODT / oral compounded | NOT FDA-approved. | NONE. No trial has ever tested it. Oral bioavailability for these peptides is a real pharmacological problem and is unpublished for this product. |
The evidence is strong exactly where it was gathered and silent everywhere else. The gap between those two things is where most of the marketing in this industry operates, and recognising it is the single most useful skill a patient in this market can have.